Showing 17 results for Test
S. M. Haeri, N. Sadati and R. Mahin-Rousta,
Volume 20, Issue 2 (4-2001)
Abstract
In this research, behaviour of clayey soils under triaxial loading is studied using Neural Network. The models have been prepared to predict the stress-strain behaviour of remolded clays under undrained condition. The advantage of the model developed is that simple parameters such as physical characteristics of soils like water content, fine content, Atterberg limits and so on, are used to model the stress-strain behaviour of clays under triaxial loading, without performing exact and time-consuming tests on samples.
Results from the network show that neural network is a good tool for prediction of stress-strain behaviour of clayey soils using simple physical characteristics of such soils
M. K. Jafari, M. Davoodi and M. Razzaghi,
Volume 22, Issue 1 (7-2003)
Abstract
There is a worldwide interest in the proper design of embankment dams to resist earthquake loadings. For the first time in Iran, a complete ambient vibration survey due to low-level loads such as wind, machinery activities, low level tectonic activities, and water exit from bottom outlet was performed on Marun embankment dam. These kinds of ambient vibration tests are suitable for manifesting the lower vibration modes of the dam body. Using different signal processing methods such as Power Spectra Density, the results of in-situ tests have been used to evaluate the natural frequencies, mode shapes and modal damping of the dam body. Besides ambient vibration tests, the 3-D modal analysis of the dam body was performed using ANSYS software. The foundation and abutment flexibility effects on dynamic characteristics of the dam body was investigated and the dynamic soil properties were used from Engineer’s report and some empirical relations. Also initial shear modulus of the dam body and foundation materials were evaluated by refraction survey. In this paper, the test procedures, related signal processing results, numerical analysis results and its comparison with the dynamic characteristics of the dam body obtained from the full-scale dynamic tests will be presented. Finally, calibrating procedures of the numerical model (based on increasing the accuracy of dam body geometry, soil and rock material parameters and foundation and abutment flexibility) will be discussed.
Keywords: Embankment Dam, Dynamic Characteristics, Ambient Vibration Test, Modal Analysis
A. Eslami, M. Karimpoor Fard and N. Shariatmadari,
Volume 24, Issue 1 (7-2005)
Abstract
In recent years, determining bearing capacity of piles from in-situ testing data as a complement to static and dynamic analysis has been used by geotechnical engineers. In this paper, different approaches for estimating bearing capacity of piles from SPT data are studied and compared. A new method based on N value from SPT is presented. Data averaging,
failure zone and plunging failure of piles are revisited in the light of this new method. A data bank was compiled including 42 full scale pile load tests in sites where SPT was performed close to pile locations. Comparison of current methods by error investigation with statistical and cumulative probability approaches demonstrates that the new method predicts pile capacity with more accuracy and less scatter than others. Therefore, it can be applied as a suitable solution in geotechnical design.
M. Asgaree and M. S. Seif M.,
Volume 24, Issue 1 (7-2005)
Abstract
The present paper contains the test results of a planing catamaran model. The aim of the tests was to study the effect of hydrofoil in these types of crafts. First, experiments were carried out on the bare body (i.e. without hydrofoils) to obtain non-dimensional hydrodynamic resistance coefficient versus speed. Then, the model with hydrofoils, by various locations and attack angles were subjected to tests and the results were compared with those from the tests with the bare body. Results show that
great reduction in hydrodynamic resistance of hydrofoil-supported catamaran is accessible especially at high speeds. In addition, hydrofoils positioning is important and un-suitable designs may result in instability in motion and increased in hydrodynamic resistance.
A. R. Safari, M. Ghayour, and A. Kabiri,
Volume 25, Issue 1 (7-2006)
Abstract
It is empirically established that, due to a number of factors involved, a classical (linear) analysis of buckling pressure is impossible. Nonlinear theories of buckling are, therefore, required that involve effective factors such as imperfections and welding effects. In this study, models are developed which are as close to allowable standard deviations as possible. In the next stage, their buckling behavior is investigated both experimentally and numerically using finite element packages ADINA, ANSYS, COSMOS, and MARC based on specific capabilities of each. Results show that reasonable estimates of real buckling pressure will become possible when material and geometrical nonlinearities and initial imperfections are introduced into the analytical system. Finally, in the light of the results obtained, a submarine pressure hull is analyzed.
H. Zamani and S. Ziaiee Rad, ,
Volume 26, Issue 1 (7-2007)
Abstract
An approximate numerical mthod is presented for analysis and determination of modal characteristics in straight, pretwisted non-unifom helicopter blades. The analysis considers the coupled flapwise bending (out of plane), chordwise bending (in plane), and torsion vibration of both rotating and non-rotating blades. The proposed method is based on the integral expansion of Green functions (structural influence functions) to develop the equations of motion for a clamped-free blade. Several examples are presented in various states such as flapwise bending, coupled bending-bending, coupled bending-torsion, and coupled bending-bending-torsion vibration analysis. The results obtained were compared with available numerical results in the literature. A modal testing and modal analysis were also carried out on a typical helicopter blade in static condition and the results were compared with the numerical ones. The results indicate that the proposed method is fast and robust and can be used for modeling of turbomachine blades, aircraft propellers and helicopter rotor blades.
F. Hosseinabadi, S. M. Zebarjad, M. Mazinani, V. Kiani, H. R. Pourreza,
Volume 30, Issue 2 (12-2011)
Abstract
In this article, the role of nano-size calcium carbonate in penetration resistance of medium- density polyethylene (PE) was investigated through experiments. In order to study the penetration resistance of PE and its nanocomposites, perforation test was carried out. The results of tests showed that penetration resistance depends strongly on calcium carbonate amount. As a matter of fact, addition of CaCO3 to PE increases resistance against penetration as CaCO3 amount reaches to 5 percent of weight. Stereomicroscope was used to evaluate the damage and plastic zone around the perforated area in all the samples including neat polyethylene and its nanocomposites. The plastic zone was measured using an image analysis as an effective technique. The results of image analysis techniques proved that the addition of calcium carbonate to PE makes a damaged zone around the perforated area. The results of microscopic evaluations showed that the area of plastic zone rises as the amount of calcium carbonate increases up to 7.5 percent of weight. By increasing the amount of CaCO3, resistance against penetration decreases more and some micro cracks appear around the perforated area. For further clarification of the fracture mechanism of MDPE nanocomposites, scanning electron microscopy was employed. Fracture surface images showed that when calcium carbonate is higher than 5 percent of weight, agglomeration of nanoparticles occurs, resulting in lower resistance against penetration to the samples.
A. Azimi Dastgerdi, F. Ashrafizadeh, M. R. Toroghinejad, F. Shahriari , H. Zahraei,
Volume 30, Issue 2 (12-2011)
Abstract
In this paper, bare spot defects in hot-dip galvanized sheets were studied in terms of the microstructure and their influence on the corrosion and mechanical properties. Surface characteristics and microstructural features were examined by scanning electron microscopy equipped with energy dispersive spectroscopy microanalysis system. The results showed that the major cause of the bare spots was the lack of wetability of the sheet surface due to contamination, improper heat treatment or chemical composition. Corrosion resistance was evaluated by standard salt spray test. Mechanical properties were examined by tensile testing. The time to red rust was much shorter on the bare spots as compared to other regions, but it appeared that bare spot defects had no significant effect on the mechanical properties of the galvanized steel sheets.
H.r. Salehi, S.m.r. Khalili,
Volume 30, Issue 2 (12-2011)
Abstract
In the present work, thermal and mechanical behaviors of phenolic resin are investigated. This polymer can be used as a matrix for carbon-carbon composites. To find out the best heating process, five different cycles are used for curing the polymer and flexural strength of the specimens are obtained. The cycle with maximum strength is used for the next steps. Then, the oxidation behavior of specimens is studied at different temperatures. The results show that the polymer can withstand temperature about 350°C without significant weight changes. Carbonization of phenolic resin is studied by four different cycles at 1100°C. Oxidation of carbon obtained from carbonization cycle is analyzed extensively and shows no weight change until 550°C. The microstructure of specimens is also investigated by SEM. By additining SiC micro particles to phenolic polymer, the strength change is achieved.
H.r. Salehi, S. Salami, M. Atarian, O. Ozhdelnia,
Volume 32, Issue 1 (6-2013)
Abstract
Carbon fiber composite is one of the most important materials in aerospace engineering applications. For fabrication of this composite, optimum polymerization and carbonization cycles of phenolic resin were obtained [1]. Then, carbon/phenolic composite was fabricated by mixing different weight percentages of T700 carbon fiber with phenolic resin, and the flexural strength of specimens was examined.The samples were pyrolyzed at 1100°C to form high temperature phenolic matrix. Because of high porosity of samples, the composite was impregnated to increase the density and reduce porosity. The maximum flexural strength of samples was obtained with 40 wt. % of fiber. With addition of TiO2 and ZrO2 nanoparticles to carbon/phenolic composite, thermal and mechanical improvement was measured. The samples were examined by ablation test and microstructures of composites were analyzed by SEM.
B. Khorrami Mokhori, A. Shafyei,
Volume 35, Issue 4 (2-2017)
Abstract
In this research titanium nitride (TiN) films were prepared by plasma assisted chemical vapor deposition using TiCl4, H2, N2 and Ar on the AISI H13 tool steel. Coatings were deposited during different substrate temperatures (460°C, 480 ° C and 510 °C). Wear tests were performed in order to study the acting wear mechanisms in the high(400 °C) and low (25 °C) temperatures by ball on disc method. Coating structure and chemical composition were characterized using scanning electron microscopy, microhardness and X-ray diffraction. Wear test result was described in ambient temprature according to wear rate. It was evidenced that the TiN coating deposited at 460 °C has the least weight loss with the highest hardness value. The best wear resistance was related to the coating with the highest hardness (1800 Vickers). Wear mechanisms were observed to change by changing wear temperatures. The result of wear track indicated that low-temprature wear has surface fatigue but high-temperature wear showed adhesive mechanism.
M.r. Khanzadeh Gharah Shiran, H. Bakhtiari, M. Mohammad Javadi,
Volume 36, Issue 3 (11-2017)
Abstract
In this research, the effect of standoff distance and explosive material thickness on metallurgical features of explosive welding connection of copper to 304 stainless steel has been investigated. Experimental analysis were performed using optical microscopy, scanning electron microscopy, microhardness test and tensile shear strength test. The results indicated that due to severe plastic deformation in welding, both grain elongation and refinement occurred near the connection. Also, increasing of welding parameters led to an increase in the locally melted zones. The results showed that chemical composition of the melted zone consisted of elements of both flyer and base plates. By decreasing the explosive material thickness and standoff distance, the hardness of copper interface zone decreased from 103.4 HV to 99.8 HV. Moreover, increasing the temperature in stainless steel connection led to decreased hardness. As such, the maximum tensile shear strength of 244 MPa was observed in the sample with 79 mm explosive thickness and 3 mm standoff and the minimum tensile shear strength of about 208 MPa in the sample with 46 mm explosive thickness and 3 mm standoff. By decreasing explosive thickness and standoff, the bond strength decreased, too.
H. Rashtchi, M. Shamanian, K. Raeissi,
Volume 36, Issue 4 (3-2018)
Abstract
Stainless steel bipolar plates are preferred choice for use in Proton Exchange Membrane Fuel Cells (PEMFCs). However, regarding the working temperature of 80 °C and corrosive and acidic environment of PEMFC, it is necessary to apply conductive protective coatings resistant to corrosion on metallic bipolar plate surfaces to enhance its chemical stability and performance. In the present study, by applying Ni-Mo and Ni-Mo-P alloy coatings via electroplating technique, corrosion resistance was improved, oxid layers formation on substrates which led to increased electrical conductivity of the surface was reduced and consequently bipolar plates fuction was enhanced. Evaluation tests included microstructural and phase characterizations for evaluating coating components; cyclic voltammetry test for electrochemical behavior investigations; wettability test for measuring hydrophobicity characterizations of the coatings surfaces; interfacial contact resistance measurements of the coatings for evaluating the composition of applied coatings; and polarization tests of fuel cells for evaluating bipolar plates function in working conditions. Finally, the results showed that the above-mentioned coatings considerably decreased the corrosion and electrical resistance of the stainless steel.
A. Sheikhali, M. Morakkabati, S. M. Abbasi,
Volume 38, Issue 1 (6-2019)
Abstract
In this paper, in order to study the flow behavior and elongation of as-cast ingots of SP-700 titanium alloy, hot tensile test was done in α/β dual phase and β single phase regions using strain rate of 0.1 s-1. Results showed that the hot tensile behavior of SP-700 in the α/β dual phase region (700-900 ºC) was different from the β single phase one (950-1100 ºC) due to the nature of alpha and beta phases and their crystallographic structure. This was since the number of slip systems and deformation mechanism in HCP structure were different from those in BCC structure. Beside, the intensive variation of elongation in microstructural studies showed that the dominant mechanism of hot tensile deformation of SP-700 alloy was dynamic recovery (DRV). Thus, serration of grain boundaries and occurrence of DRV were the reasons for the increase of elongation with the rise of temperature. However, beta grains growth and occurrence of grain boundary fracture made a slight decrease in elongation in the temperature range of 1000-1100 ºC.
R. Amirarsalani, M. Morakabati, R. Mahdavi,
Volume 40, Issue 1 (5-2021)
Abstract
In this research, the hot deformation behavior of W360 tool steel was investigated using hot compression test at 1000-1200°C and strain rates of 0.001, 0.01, 0.1, and 1 s-1. According to the results, dynamic recrystallization was found the most important restoration factor of this alloy during hot deformation. Recrystallization was enhanced with an increase in temperature and strain rate. Also, the hot working process was optimized by drawing the processing map of this steel. Microstructural images obtained from the hot compression test showed that recrystallization started at 1000°C and the strain rate of 0.01 s-1 and developed with increasing temperature and strain rate due to an increase in the stored energy and suitable regions for nucleation. The results of drawing the processing map showed that the best hot deformation region was the temperature range of 1050-1150°C and strain rates of 0.1-1 s-1.
M. Kamali Ardakani , M. Morakabati,
Volume 40, Issue 2 (9-2021)
Abstract
The aim of this study was to investigate the behavior of hot deformation and occurrence of restoration phenomena during the deformation of AISI H10 hot work tool steel. For this purpose, hot tensile test was performed on the steel in the temperature range of 900-1150 ºC with a temperature interval of 50 ºC and at a constant strain rate of 0.1s-1. The microstructures were examined and the curves of hot flow and ductility were drawn. According to the curves and microstructures, ductility was lower at temperatures of 900 ºC and 950 ºC due to inactivity of repair processes and the presence of carbides. Ductility increased in the temperature range of 1000-1100 ºC due to the occurrence of dynamic recrystallization. Finally, ductility decreased in the temperature of 1150 ºC due to the dissolution of carbide particles and grain growth. The results obtained from hot tensile test and microstructural studies at a constant strain rate of 0.1s-1 revealed that the appropriate temperature range for deformation of AISI H10 hot work tool steel was 1000-1100 ºC.
M. Ghalambaz, M. Shamanian, A. M. Eslami, M. Abdollahi, E. Abdoulvand,
Volume 41, Issue 1 (8-2022)
Abstract
This research investigated the bonding properties of AISI 321 austenitic stainless steel from microstructural, mechanical, and corrosion points of view. To obtain the optimal parameters of pulsed current gas tungsten arc welding (PCGTAW), the Taguchi method was used. A cyclic potentiodynamic polarization test evaluated the corrosion resistance of the welded samples. The optimal conditions were achieved when the background current, the pulse current, the frequency, and the percentage of the pulse on time were 50 amps, 140 amps, 5 Hz, and 50, respectively. On the other hand, the analysis of variance showed that the percentage of pulse on time equal to 36 and the background current equal to 46 amperes were the most influential factors on the surface current density of the austenitic stainless steel 321 connection using the PCGTAW process. The mechanical properties were assessed using punch shear testing. In the optimal condition, the maximum shear force and strength were 3200 N and 612 MPa, respectively. The results showed that the most critical factor affecting the bonding properties of 321 steel was the heat input.
